The present application relates to power semiconductor devices, methods, and structures, and more particularly to those using predominantly vertical current flow.
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
Trench Schottky Barrier Diodes (“SBD”s) such as shown in FIG. 1A are widely used in many power conversion applications such as dc-dc converters. In applications where the transistor may be forward biased—i.e. where the source terminal is more positive than the drain terminal, in an n-channel device—the Schottky Barrier Diode provides a diode which can be used as the “free-wheeling diode” in many converter topologies. Often the Schottky Barrier Diode is electrically connected in parallel with the body junction, since the Schottky Barrier Diode provides a lower forward voltage drop, and avoids minority carrier injection. The Schottky Barrier Diode will also typically have a lower stored charge in reverse recovery, which reduces switching losses in circuits which include forward-bias phases.
It is desirable that Schottky Barrier Diodes provide low forward voltage drop to reduce power losses. Trench Schottky Barrier structures such as shown in FIG. 1A suffer from relatively higher leakage current at reverse bias. This drawback is especially important for monolithically integrated MOSFET-SBD structures such as Trench MOSFET Barrier Structures (TMBS).
New power MOSFET structures were disclosed for example in US published patent applications 2008/0073707 and 2009/0206924, and in provisional applications 61/326,210 and 61/334,573, all of which are hereby incorporated by reference. These applications variously disclosed Recessed Field Plate (RFP), Embedded Field Plate (EFP), and Embedded Shielded Field Plate (ESFP) structures. Such MOSFET structures provide low specific on-resistance, lower gate-drain charge Qgd, and lower gate charge Qg.